The invention relates generally to endoprostheses and, more specifically, to an intraluminal stent for repairing a damaged or diseased artery, or to be used in conjunction with a tube graft for delivery to an area of a body lumen that has been weakened by damage or disease, such as an aneurysm of the abdominal aorta. Several areas of the body are particularly suitable for receiving an endoprosthesis, commonly referred to as an intraluminal stent to hold open and insure the patency of a body lumen. Two such areas include the coronary arteries and the aorta, especially in the area where an aneurysm has developed.
An abdominal aortic aneurysm ("AAA") is an abnormal dilation of the arterial wall of the aorta in the region of the aorta that passes through the abdominal cavity. The condition most commonly results from atherosclerotic disease. Frequently, abdominal aortic aneurysms are dissecting aneurysms, that is aneurysms that are formed when there is a tear or fissure in the arterial lining or wall through which blood is forced and eventually clots, forming a thrombosis which swells and weakens the vessel. Abdominal aortic aneurysms do not cause pain, but are easily detected in a thorough physical examination. If the aneurysm is not detected and treated, it is likely to rupture and cause massive hemorrhaging fatal to the patient.
Treatment of AAAs comprises some form of arterial reconstructive surgery which commonly is referred to as a "triple-A" procedure. One such method is by-pass surgery, in which an incision is made into the abdominal cavity, the aorta is closed off above and below the site of the aneurysm, the aneurysm is resected, and a synthetic graft or tube sized to approximate the diameter of the normal aorta is sutured to the vessel to replace the aneurysm and to allow blood flow through the aorta to be reestablished. The graft commonly is fabricated of a biocompatible material that is compliant and thin-walled. Nylons and synthetic fibers such as those manufactured under the trademarks DACRON or TEFLON have been found to be suitable for the construction of the graft. Studies have shown that the mortality rate associated with this surgical procedure is favorable (less than 5%) when it is performed prior to rupture of an aneurysm. However, patients having an AAA typically are over 65 years of age, and often have other chronic illnesses which increase the risk of perioperative or post-operative complications. Those patients thus are not ideal candidates for this type of major surgery. Further, it has been pointed out that this procedure is not often successfully resorted to after an aneurysm has ruptured (the mortality rate increases to over 65%) because of the extensiveness of the surgery and the time required to prepare a patient for it.
Because of the aforementioned disadvantages to conventional surgical methods, another procedure was developed as an alternative to conventional, major surgery. This method also involves emplacement of a graft at the site of the aneurysm; however, the graft is deployed there by being routed through the vascular system carried by a catheter, wire or other device suitable for negotiating the vasculature. The graft and its deployment system often are introduced into the blood stream percutaneously with a femoral approach and the entire procedure can be performed using local rather than general anesthesia.
Once the graft has been positioned at the aneurysm, it is disengaged from the delivery system and can be affixed to the aortic wall both distally and proximally of the aneurysm. For this purpose, grafting systems usually include fixation means such as staples or hooks which can be manipulated and driven into the intima of the vessel via some mechanical feature of the system, or by some physical process, such as expansion of the graft through application of pressure. To avoid premature detachment of the graft and to prevent the attachment elements from damaging the vessels or halting the forward movement of the system while the graft is being routed to the treatment site, the systems often are provided with a feature such as a capsule or a sheath that protects and contains the graft until such time as deployment is desired.
Once the graft is in place, it is positioned in the vessel spanning the site of the aneurysm such that the walls of the graft are generally parallel to the walls of the affected area of the aorta. The aneurysm thus is excluded from the circulatory system by the graft rather than being resected altogether. If the aneurysm is a dissecting type and a thrombosis exists between the walls of the aorta, the now-excluded aneurysm may beneficially provide structural support for the graft.
Grafting systems are known that include what commonly is referred to as an attachment system for deploying the graft. The attachment system is a tubular device which is fitted inside and is generally coaxial with the graft, and which can extend out of the graft at either or both the proximal and distal ends thereof. The attachment system often has a lattice-like or open weave structure, which provides it with flexibility and which promotes rapid endothelial tissue growth through the structure once the graft has been deployed. It may be provided with additional hook-like elements for penetration of the intimal walls for attachment of the graft to the aorta, or those hook-like elements may be provided on the graft itself. Graft systems of type described can be found in U.S. Pat. Nos. 4,787,899 (Lazarus); 5,104,399 (Lazarus); 5,219,355 (Parodi et al.); and 5,275,622 (Lazarus), which are incorporated herein by reference. A stent and graft combination can be found in U.S. Ser. No. 340,112, filed Nov. 15, 1994, which is commonly assigned to the same assignee as the present invention, namely Advanced Cardiovascular Systems, Inc., Santa Clara, Calif. U.S. Ser. No. 340,112 also is incorporated herein by reference. Generally, prior art systems that employ attachment means which include hooks or staples create a very large profile for delivery through a body lumen.
The actual function of delivering the graft may be accomplished by inflating a balloon of a catheter by introducing pressurized fluid into a lumen of the catheter from a source external to the patient. Inflation of the balloon applies a force to the graft and any attachment system supplied therein which extends radially and presses the graft and attachment system into the vessel wall just above and just below the aneurysm. Other devices used to attach a graft to the aortic wall for AAA repair include intravascular stents of the type found in U.S. Pat. No. 5,316,023.
In order for a stent to be used most advantageously with a graft deployment system for treatment and repair of aneurysms, the stent must be composed of a biocompatible material and must be simultaneously flexible enough to comply with the catheter or other element used to route the graft through the often tortuous vascular path to the site of the aneurysm and strong enough radially to maintain the opening in the graft once delivered. It is important that the stent or stent-and-graft combination have a low profile for intraluminal delivery. The stent must be well suited to deployment by a delivery system that is not overly complex, and thus is reliable and easy to operate. Further, it is desirable that the stent be expandable, so that upon application of a force or physical change from within sufficient to cause radial expansion, it encourages affixation of itself and the graft to the aortic walls. Although various stents have been proposed, none adequately provides all of these desirable features.
Another area in which stents have commonly been used are in the coronary arteries for the purpose of repairing a damaged or diseased vessel. In typical prior art situations, the stent is mounted on the balloon portion of a catheter and is delivered intraluminally by known methods to a specific location in a coronary artery. Generally, a stent is deployed after a patient has undergone a PTCA (percutaneous transluminal coronary angioplasty) procedure in which a lesion or other obstruction in the artery has been dilated by known methods. Deploying an intravascular stent at the site where an angioplasty has occurred will reduce the likelihood of a restenosis and can assist in tacking up any dissections and in general reinforce the vessel wall.
Most, but not all, stents currently described in the art provide a smooth outer wall surface which, when expanded, do not penetrate into the vessel wall. Thus, some prior art stents do not provide adequate fixation methods to attach the stent to the vessel wall during deployment.
What has been needed and heretofore unavailable is a stent for use in combination with a graft which has a high degree of flexibility for efficient advancement through tortuous passageways, which can be radially expanded from a relatively small diameter and low profile to a relatively large diameter without substantial longitudinal contraction, and which exhibits mechanical strength sufficient to penetrate the vessel walls thereby resisting migration and to maintain the patency of a synthetic graft implanted at the site of an aneurysm. The present invention satisfies this need.